The present invention relates to a transmission between a power input and an output shaft, especially for a motor vehicle, of the kind comprising a speed variator having a primary pulley and a secondary pulley and a planetary device with four elements, in which a permanently active input element is connected to the power input by means of the speed variator, whilst a likewise permanently active output element is connected to the output shaft, each of the two remaining elements, called the first and second switching elements, being adapted to be made either active or passive by control means which make one of the switching elements active while the other is passive, and vice versa.
A switching element is said to be made active when it is connected to a member which is outside the planetary device and which is given a drive or resistant torque. In the first case, it is coupled, for example by means of a clutch, to the power input. In the second case, it is locked, especially by means of a brake which acts between it and a fixed structure. The switching element is said to be made passive when it is uncoupled from any member outside the planetary device, that is to say when it is left idle.
The speed variator can be of any suitable type, for example mechanical with pulleys of variable spacing and a belt, or hydraulic, with two units, of which one, the transmitting unit, constitutes a motor, whilst the other, a receiving unit, constitutes a pump, or electrical, etc. Such a speed variator makes it possible to establish a speed ratio and a torque ratio which are continuously variable between the primary and the secondary of the speed variator, this occurring in either direction of transmission.
The planetary device having four elements, with a permanently active element, a likewise permanently active output element and two switching elements, one of which is active while the other is passive, and vice versa, makes it possible, in association with the speed variator, to give the transmission good performances, especially as regards the dimensions of the variator, its useful life, the transmission efficiency and the extent of the speed ratios of the transmission, this being so, in particular, with two ranges of forward motion and one range of reverse motion.
These ranges of forward and reverse motion are obtained manually and/or automatically as a result of control of the clutches and brakes associated with the switching elements.
Transmissions of the kind described above, which have been proposed hitherto, give interesting results, but with an operation during which the rotational speed of the output element or of one of the switching elements is still too high to be fully satisfactory, whilst the construction is somewhat complex and bulky, with three separate parallel axes, two of which are those of the primary and the secondary of the speed variator, whilst the third is that of the planetary device.
The subject of the present invention is a transmission between a movement take-off and a receiving shaft, especially for a motor vehicle, of the type mentioned above, which is free of these disadvantages and the operation of which is excellent, with good ranges both of forward motion and of reverse motion, whilst ensuring rotational speeds of the various elements of the planetary device which are always moderate, and a simple and convenient construction of little bulk.